1. Field of the Invention
The present invention relates to a technique of generating a high-resolution image from multiple low-resolution images.
2. Description of the Related Art
The user of a digital video camera (hereafter may simply be referred to as ‘video camera’) often demands to capture one scene or frame during reproduction of a moving picture and generate a higher-resolution image than the resolution of the image of the captured frame (hereafter referred to as the ‘frame image’). Here the terminology ‘resolution’ means the density of pixels or the number of pixels included in one image.
One typical method of generating the higher-resolution image combines multiple low-resolution images. Combination of multiple low-resolution images is expected to enhance the quality of a resulting composite image, compared with simple resolution conversion of only one image.
For example, a proposed technique in Japanese Patent Laid-Open Gazette No. 2000-244851 selects one frame image as a base frame image among (n+1) consecutive frame images, computes motion vectors of the residual n frame images (subject frame images) relative to the base frame image, and combines the (n+1) frame images based on the computed motion vectors to generate one high-resolution image.
Images of multiple frames included in the moving picture may have a ‘positional shift’ or a ‘motion’. Here the ‘positional shift’ represents a positional change between multiple frames that is eliminated by uniformly moving the whole image, for example, an image shift due to an unintentional hand movement. The ‘motion’ mainly represents movement of a certain subject in the image, that is, a local change in the image. The motion includes both a direct movement of a subject, such as a person or an automobile, and a relative movement of the subject due to a parallax caused by a moving camera.
The prior art technique gives consideration to the motion between the multiple frames in the moving picture (corresponding to the ‘positional shift’) but does not take into account the motion in the moving picture. A resulting composite image may accordingly have an undesirable image overlap of an identical image part with motions. There is accordingly a demand to generate a high-resolution still image from multiple low-resolution frame images included in a moving picture without causing any image overlap of an identical image part with motions.
This problem is not intrinsic to composition of multiple low-resolution images included in a moving picture but is generally found in composition of multiple low-resolution images arrayed in a time series.